Current methods for completing or re-completing hydrocarbon wells may involve pumping very large volumes of propant into one or more production zones of the well. More than 10,000,000 pounds (4,555,000 kg) of propant (e.g., frac sand, sintered bauxite, or ceramic pellets) mixed with a fracturing fluid such as “slick water” may be pumped through a frac head and down a production casing into production zone(s) of the hydrocarbon well at rates of 300+ barrels/minute during a well stimulation procedure. As understood by those skilled in the art, pumping millions of pounds of abrasive propant through known frac heads at high rates causes erosion, commonly referred to as “wash”, in those frac heads.
The construction and maintenance of frac heads requires skilled labor and expensive alloy steel (e.g. 4140 steel). In order to reduce the cost of maintaining frac heads, abrasion-resistant frac heads with hardened steel inserts were invented, as taught for example in applicant's U.S. Pat. 7,213,641 which issued May 8, 2007. Abrasion resistant frac heads significantly reduce frac head maintenance, but do not eliminate it. Because hardened steels are brittle, they cannot be used to line a bottom end of a central passage through the frac head, which is subject to impact and compression forces. Consequently, even abrasion-resistant frac heads require maintenance in addition to the replacement of the hardened steel inserts. To facilitate such maintenance, multipart frac heads with replaceable components were invented, as described in Assignee's co-pending published patent application 2008/0257540 filed Apr. 17, 2007 and published on Oct. 23, 2008, the entire specification of which is incorporated herein by reference.
FIG. 1 is a schematic cross-sectional diagram of one embodiment of Assignee's multipart frac head 100 described in the above-identified co-pending patent application. The multipart frac head 100 has a frac head body 102 and a plurality of entry ports, two of which (104a, 104b) are shown. Frac heads are generally equipped with 2-5 entry ports. In this embodiment side entry ports 104a, 104b are welded to the frac head body 102 using methods known in the art. Each side entry port 104a, 104b includes a respective central bore 106a, 106b in fluid communication with a mixing chamber 108 of the frac head body 102. A top end of each side entry port 104a, 104b supports a frac iron adapter 112a, 112b that is also known in the art.
The frac head body 102 has a top end 118 with a central passage 120 in fluid communication with the mixing chamber 108. In this embodiment, the top end 118 terminates in a threaded union described in Applicant's U.S. Pat. No. 7,125,055 entitled Metal Ring Gasket for a Threaded Union, which issued on Oct. 24, 2006, the specification of which is incorporated herein by reference in its entirety. The threaded union connector is compatible with a complementary threaded union connector 128 of equipment connected to the multipart frac head 100. The equipment is typically a high-pressure valve, but may be any other well completion, re-completion or workover equipment.
A bottom of the mixing chamber 108 has a funnel-shaped section that tapers inwardly to a central passage 132 of a bottom leg 134 secured to the frac head body 102. The tapered bottom end of the mixing chamber 108 is lined with a wear-resistant insert 146. A lock nut 150 secures the bottom leg 134 in the frac head body 102. A bottom end of the bottom leg 134 terminates in a threaded union connector described in Applicant's above-referenced U.S. Pat. No. 7,125,055.
Although Assignee's multipart frac heads with replaceable components has significantly reduced maintenance costs, further improvements are desirable.
There therefore exists a need for a frac head that is more quickly and easily constructed and is yet more erosion resistant than known prior art frac heads.